With automatic test equipment becomes part of the overall process electronic assembly , DFT must include not only the use of traditional hardware , but also the knowledge test equipment diagnostic capabilities .
For the sake of design test (DFT, design for test) is not a single personal thing , but a team of engineering, test engineering , manufacturing department on behalf of the Department of Design and procurement work composed . Product design and engineering capabilities must be specified tolerance requirements . Must provide a test project at the lowest cost , with minimal rework reached only as high as first pass yield (FPY, first-pass yield) strategy. Manufacturing and Quality Department must provide the cost of production inputs, similar products in the past what has been done , what is not done , as well as relevant for the sake of production design (DFV, design for volume) to help improve yields . Purchasing Department must provide accessible components, especially the reliability of the information . Test Department and Purchasing Department at the time of purchase on board (on-board) test hardware components must work together to ensure that these components are available and easy to implement . Usually as a test system to collect data about the history of the use of sensors , process improvement achieved , this should be the quality of the target group . So these functions should be placed / removed before the completion of any node selected.
Parameters in a test environment before formulating policy , preparation and understanding is crucial. Parameters that affect the testing strategy include : accessibility. Full access and large manufacturing test pads are always the target for the design of the circuit board . Usually do not provide full access for four reasons :
Board size . Design smaller ; question is " extra" board space test pad. Unfortunately , most of the design engineers believe accessibility welding test printed circuit board (PCB) less important things . Because when you can not use online tester (ICT, in-circuit tester) simple diagnostic product must by design engineers to debug , the situation would be another matter. If you can not provide full access , testing options are limited .
Function. Lost in some high-speed design performance impact plate , but you can gradually reduce the impact on the product testability .
Board size / number of nodes . This is when the physical size of the board have any existing equipment can not be tested . Fortunately, this problem can increase the budget or use external test equipment on the new test facility to be resolved. When the number of nodes is greater than the existing ICT, problem harder to solve . DFT team must understand the test methods that will allow the manufacturing sector with a minimum of time and money to output a good product. Embedded self-test , boundary scan (BS, boundary scan) and function blocks tests can be done . The diagnosis must support unit under test (UUT, unit under test); This test method can only be used by the existing test equipment and capabilities , and fault spectrum manufacturing environment can only be done in-depth understanding .
DFT rule does not comply with or understand. Historically , DFT rules understood by the manufacturing environment , a process engineer or team of engineers and functional test requirements and component technologies enforcement. In a real environment , the process is lengthy , requiring mutual communication design , computer-aided design (CAD) and between tests . The pan- flavored repetitive tasks prone to human error , often due to reach the market in time (time-to-market) pressure while passing by . Now the industry has started using automatic " produce Analyzer ", using DFT rules to evaluate CAD files. When a contract manufacturer (CM, contract manufacturer) to use, can be classified several sets of rules. Continuity and product evaluation error rule is an advantage of this method.
DFT team tests the availability of equipment should be clear existing test strategies. With OEM steering CM rely more and more , are the differences between the use of plant and plant. Manufacturers do not clearly understand the process , may use too much or too little testing. Existing test method comprising :
Manual or automatic visual test to confirm the components on the PCB Mount use of visual and comparison. There are several methods to implement this technique :
Manual Vision is the most widely used online test , but due to manufacturing production increased and reduced board and components , this approach becomes feasible. Its main advantage is low cost and no pre- test fixture , and its main drawback is the high cost of long-term , non-contiguous defects found , data collection difficulties , without limitation electrical testing and visual .
Automated optical inspection (AOI, automated optical inspection), before and after reflow usually use the newer method of manufacturing defects confirmed . It is non- electric , non- fixture , online technology , the use of "study and comparison (learn and compare)" program to make loading (ramp-up) time to a minimum. Automatic visual polarity , component presence and absence of checks is better, as long as the original components behind the " science" of elements similar to . Its main advantage is the easy-to- follow diagnosis , quick and easy application development , and no fixture. Its main disadvantage is shorted to identify the poor , not the high failure rate and electrical testing .
Automated X- ray inspection (AXI, automated X-ray inspection) is currently the only method of testing a ball grid array (BGA, ball grid array) weld quality and obscured solder balls . It is the early discovery process defects , non-electrical , non-contact technology , reducing the work process (WIP, work-in-process). Progress in this area , including pass / fail diagnostic data and component level . AXI There are two main methods: a two-dimensional (2-D), see the complete board , three-dimensional (3-D), a plurality of images taken at different angles . Its main advantage is the only BGA welding quality inspection tools and embedded components , no fixture costs. Its main disadvantage is slow , high failure rate , detection solder rework difficult , high cost per plate , and a long development time .
Manufacturing defects analyzer (MDA, manufacturing defect analyzer) is a high yield / low good tool for mixed environments , where the test is used only for diagnostic manufacturing defect. When no residual reduction technology , repeatability between testing machine is a problem . There , MDA no digital drives, components or firmware programming board test (firmware) on can not function. Test time is less than the visual test , so to catch up tempo MDA production line . This method uses a needle bed , so you can then diagnostic output . The main advantage of lower upfront costs , lower WIP, programming and program maintenance of low cost, high output , easy to follow diagnosis, and fast short-circuit and open-circuit test completely . Its main drawback is that the material can not be confirmed list (BOM, bill of material) meets the measurement unit (UUT, unit under test), no digital confirmation , no functional testing capabilities , you can not call the firmware (firmware), is usually not covered by the test instructions , repeatability, cost of board and board fixture between the lines , and the use of problem.
ICT will identify manufacturing defects and test analog, digital, mixed-signal components together to ensure that they meet specifications. Many devices have a programming board (on-board) memory capacity , including the serial number, pass / fail and system data (genealogy data). Some devices makes the program easier to produce , it is through the graphical user interface tool embedded (GUI, graphical user interfaces), easy to use and store the code to a special file to make it possible to achieve the multi-version test and firmware (firmware) transform easily the . Some devices have a complex instrumentation , the interface function will confirm the UUT , and the available commercial instrument . Now test equipment with embedded computer-aided design (CAD) interface and a non- diversified environment to reduce development time. Finally, some UUT test machine provides in-depth coverage analysis , Cheung said it is testing or no testing of components. The main advantage of ICT is the low cost of testing each plate numbers and functional test capabilities, high output , good diagnosis, rapid and thorough testing of short-circuit and open-circuit programming firmware defect coverage to apply and easy programming. Its main drawback is that , fixtures, programming and debugging time , fixture costs, expected expenditures and usage problems.
Flying Probe Tester (flying-probe tester) has been welcomed in the past few years , thanks to advances in mechanical precision , speed and reliability. In addition , now the prototype (prototype) manufacturing, rapid conversion of low -volume manufacturing requirements , no market requirements fixture test system has made flying probe test to become the desired choice . The ability to provide the best learning program probe (learn capability) and BOM test, which automatically increase monitoring during testing . Probe software should provide an easy way to load CAD data because XY and BOM data must be used when programming . Because node accessibility side of the plate may be incomplete , so the test generation software should not be repeated automatically generated segmentation procedure. Probe using scalar (vectorless) connection technology test digital, analog and mixed-signal components ; This should be used by the user UUT both sides of the capacitor plates (capacitive plate) to complete. The main advantage of flying probe tester is that it is the fastest to reach the market time (time-to-market) tools , automatic test generation , no fixture costs , good diagnostic and ease of programming. The main drawback is the low yield, the limitations of digital coverage , fixed asset expenditures and usage problems.
Function test (functional test), it can be said is the first automated test principle , have seen the importance of revitalization . It is specific to a particular cell or a plate , can be accomplished by various . A few examples : The final product testing (final product test) is the most common functional testing methods. Finally, unit testing after assembly is spending less , reduce operating errors . However, the diagnosis is difficult or does not exist , thus increasing costs. Only testing of the final product , there is the opportunity to damage the product , if there is no provision of automated testing software or hardware protection. Final testing of the product is also slow , usually take up more space. When it is necessary to meet the standards normally do not use this method because it usually does not support parameter measurements . The main advantage of testing the final product is the lowest initial cost, once assembled , and product and quality assurance. The main disadvantages include low diagnostic resolution , lack of speed , damaging the long-term cost , FPY, find the board due to the short circuit or machine , high repair costs and non- parametric test capabilities.
New physical model (hot mock-up) is typically placed in different stages of assembly , and not just in the final test. In the diagnosis , it is better than the final product testing, but because of the need to establish specialized test unit and higher costs. Physical model tests may be faster than the final product , program debugging test only if a specific board. Unfortunately, due to the lack of protection , if there is no short-circuit diagnosis and treatment in the previous procedure may damage the test bed. Its main advantage is the low initial cost. The main drawback is the low efficiency of space utilization , maintenance cost of the test equipment , because no short circuit and damage the UUT test capability parameters .
Software control , commercially available equipment (software-controlled, commercial available instrument) is usually called the " stuffing " type test ("rack and stack" test), since the instrument is purchased separately and then connected together . Synchronize the device software is usually fully customized . Instrument can be purchased relatively integrated business solutions are not expensive , if done correctly , allows independent UUT effectiveness. But this " self-made" systems typically slower , engineering changes and production site support difficult , because these applications are internal archive (under-documented). Its main advantage is that the UUT damage protection , faster output , occupies a small space requirements , and independent / industrial acceptable verification. The main disadvantage is time consuming , difficult to support , using the updated remote facility.
Business users integrated system (commercial, custom integrated system) coupling software and hardware on a test platform , for example , IEEE, VXI, Compact PCI or PXI. File archiving, software support and standard manufacturing concept makes these systems easy to use and support. Higher upfront costs than established within the program , but the cost is adjustable , as higher performance , output and repeatability. It is also easy to produce on-site support and new product development period. The main advantage is a fast output , requires less floor space and re-set the most likely to support the best repeatability and provide commercially acceptable than independent experience. The main disadvantage is the high initial cost.
Test methods such as non-contact laser system is the latest development in PCB testing technology . The technology has been proven in the empty board (bare-board) area being considered for the mounting plate (populated board) tests. This technique only sight (line-of-sight), the non- covered access (non-masked access) to detect defects . Each test at least 10 milliseconds , fast enough for mass production line . Fast output , does not require fixtures, and sight / non- covered visit is its main advantage ; without trial production , the high initial cost, high maintenance, and use of its main drawbacks.
Test methods and defect coverage is important to develop testing strategies before to understand existing test methods and defect coverage. There are many different electrical defect coverage testing methods .
Short circuit and open circuit. MDA and ICT benefactors identify short circuit - they have reached each electrical node needle bed , measure the resistance between the dots to confirm the short circuit. Empty board testing machine ground capacitance (capacitance-to-ground) technology, if confined to an empty plate , then its efficiency and speed is high. Flying Probe test uses capacitive technology (capacitor technique) and approximate short-circuit technology (proximity shorts technique); former manufacturing facility for most of reproducibility , lack of good diagnostic . The best approximation test using the original CAD data to confirm the trace position , allowing the programmer to select the maximum distance between the test points. This test provides a degree of speed control ; however , it should be recommended that the clamp device has a functional test flow (current-clamping) cable or double fold (fold-back) to prevent damage to the board or the power supply testing machine because, by low impedance short circuit elements only during the short-circuit test may not be found .
Passive Analog (passive analog) has been confirmed UUT board and install the correct welding parameters in the process components to ensure acceptable quality . This test is often only a small number of WIP when carried out , so a lot of the products in question occurred before the problem can be corrected . No power to the board , with optional passive or active protection (guard) to the parallel current paths so that the current is zero . Protection (guard) and position around the UUT requires inlet needle bed.
Visual system provides device level (device-level) diagnosis. They use a template (golden board), it is not electrically testing the UUT compared. MDA provides electrical testing and component level (component-level) diagnostic , again compared with a known good board. ICT for electrical testing , provides device-level diagnostics , and BOM comparison values and errors. Functional testing machine according to the designer's specifications ( usually called template golden board) to be tested. If the function test thoroughly , then it can ensure that products shipped out. However, if FPY not particularly high, consideration will be the manufacturer of defective products , waste and costly manual diagnostic and repair costs.
Active analog (active analog). To board powered ICT, functional testing machines and non- needle test to find good and bad active analog components . ICT and flying probe testing, while providing pin level (pin-level) diagnosis, but can not measure some of the key manufacturer's specifications ( eg , bandwidth, input bias current, etc. ) . Functional testing machine to measure the output characteristics , without providing pin -level diagnostics. MDA With the help of scalar technology , the visual system only confirm the presence of elements. X-ray diagnostic welding quality .
Testing digital and mixed-signal components. Visual , X-ray diagnosis of MDA only open and shorted . ICT using a variety of methods , depending on the components, circuit and accessibility . It can only use scalar technology continuity , when all of the entrance of continuity and elements sure to use the BS. To create a model for a particular element may be generated by the time-consuming manual vectors , and may not cover the defects to determine the effect . Free vector technology for continuity and assurance components limited run test vectors can be used to combine strategies to make maximum coverage , while limiting development time.
Functional system test circuit in accordance with design specifications / module , but the lack of repair costs will reduce lead foot level / component level diagnostics. In most cases , the function test is not available for the process improvement requires deep data .
Manufacturing test strategy does not have a strategy , or so the manufacturer should fit . When developing a test and process improvement strategy must take into account many variables.
Confirm manufacturing defect spectrum should be a factory product specificity and particularity . These data , if it is relevant and reliable , it will reduce staff and scrap costs and increase customer confidence. Defect data should be collected, compiled and discussed at regular meetings held on the quality of the group . This data should be used to develop a test strategy to find common preventable defects. The data should include factory site and failure , date marking . Defects in new products should be monitored , and mature product should be monitored , and supplier quality improvement FPY . Defect data should be compared with the short -term inside , along with other places together to improve the overall quality. Weather conditions , personnel , suppliers, and production line tracking data should be changed because they are usually the potential quality factor .
Two important factors are the quality of the data collection and distribution of the relevant test . A sensor as the ability to improve the quality of collected data , and data managers the ability to correct the data communicated to the team division , affecting the present and future products . Define the correct data depends on the facilities and products. Testing machine acts sensor monitoring process . An effective test strategy to identify the distribution process as close to the root of the problem , reducing the number of producing bad product .
